Post on 30-Jul-2020
transcript
S1
Electronic Supplementary Information
Uncontinuously covered IrO2-RuO2@Ru electrocatalysts for
oxygen evolution reaction: How high activity and long-term
durability can meet up in the synergistic and hybrid nano-
structure?Guoqiang Li,abc Songtao Li,d Junjie Ge,*ab Changpeng Liuab and Wei Xing*ab
*Corresponding author: W. Xing, E-mail: xingwei@ciac.ac.cn
J. Ge, E-mail: gejj@ciac.ac.cn
Tel.: 86-431-85262223; Fax: 86-431-85685653
a State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China.
b Laboratory of Advanced Power Sources, Jilin Province Key Laboratory of Low
Carbon Chemical Power Sources, Changchun Institute of Applied Chemistry, Chinese
Academy of Sciences, Changchun 130022, PR China.
c University of Chinese Academy of Sciences, Beijing 100039, PR China.
d Institute of Mathematics, Jilin University, Changchun 130012, PR China
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2017
S2
1 Experimental Section
1.1 Materials
The chemical reagent H2IrCl6·xH2O (35 wt% Ir) and RuCl3·3H2O were purchased
from Sino-Platinum Metals Co., Ltd. 5 wt% Nafion® ionomer was purchased from
DuPont Co. NaBH4 was purchased from Sinopharm Chemical Reagent Co., Ltd.
NaOH, HNO3, H2SO4 and ethanol solution were purchased from Beijing Chemical Co.
and were used as received without further purification. Commercial IrO2 and RuO2
(denoted as IrO2 (CM) and RuO2 (CM), respectively) were purchased from Alfa
Aesar Chemical Co., Ltd. Commercial Pt/C (20 wt%Pt) catalyst was purchased from
Johnson Matthey Company. It should be noted that all solutions in our work were
prepared using Millipore-MiliQ water (resistivity: ρ > 18 MΩ*cm) and the reagents
used were analytical-grade.
1.2 Preparation of catalysts
The synthesis of IrO2-RuO2@Ru catalysts was proposed and accomplished through
the following procedures: taking IrO2-RuO2@Ru (1:1) as an example. The preparation
of metallic Ru was the first procedure, 0.2 mmol RuCl3·3H2O was dissolved in
distilled water to form a 30 mL solution. Then, 6 mL of aqueous NaBH4 solution (0.2
M) was quickly injected into the RuCl3 solution under vigorous stirring. The stirring
was continued for about 10 min until the entire solution became colorless. Finally, the
metallic Ru was obtained after filtered, washed and dried. Subsequently, the
preparation of IrO2-RuO2@Ru (1:1) was another procedure. Firstly, 0.2 mmol Ru was
dispersed into 40 mL deionized water ultrasonically for 1 h. After that, 0.2 mmol
S3
H2IrCl6·xH2O was added to the Ru suspension to react for another 1 h. Then, aqueous
NaOH solution (1 M) was added to the aforementioned solution and stirred for 1 h at
80 °C, this complex was precipitated by addition of HNO3 (1 M) until the pH reached
8. Finally, the IrO2-RuO2@Ru (1:1) was achieved by centrifuged, washed, dried and
annealed in air at 450 °C for 1 h. Similarly, IrO2-RuO2@Ru (2:1), IrO2-RuO2@Ru
(3:1) and IrO2-RuO2@Ru (4:1) were fabricated by varying the atomic ratios of Ir/Ru
in the feeding solutions. Moreover, Ir3RuO2 alloy oxide and pure IrO2 were prepared
through similar method.
1.3 Physical characterization
The crystallinity and phase purity of the prepared catalysts were confirmed by X-Ray
diffraction (XRD) measurements using a Rigaku-D/MAX-PC2500 X-ray
diffractometer (Japan) with the Cu Ka (l ¼1.5405 Å) as a radiation source operating at
40 kV and 200 mA. The surface elemental composition and chemical states of as-
prepared catalysts were analyzed by X-ray photoelectron spectroscopy (XPS, Kratos
Ltd. XSAM-800) with an Al Ka monochromatic source. The specific surface area was
determined through N2 gas adsorption/desorption measurements (ASAP 2020,
Micromeritics Instrument Corporation, USA), calculated by the Brunauer-Emmett-
Teller (BET) formulations. The morphologies and compositions were characterized
with transmission electron microscopy (TEM), high-resolution transmission electron
microscopy (HRTEM), high-angle annular dark-field scanning TEM (HAADF-
STEM), element mapping analysis and energy-dispersive X-ray spectroscopy (EDX)
by Tecnai G2 F20 S-TWIN electron microscope (FEI Company, USA) working at an
S4
accelerating voltage of 200 kV. Inductively coupled plasma optical emission
spectroscopy (ICP-OES; X Series 2, Thermo Scientific USA) was used to determine
the quantity of Ir, Ru dissolution after the accelerated durability tests.
1.4 Electrochemical measurements
All electrochemical tests were carried out with a Princeton Applied Research
Model273 Potentiostat/Galvanostat and a conventional three electrode
electrochemical cell at room temperature with 0.5 mol L-1 H2SO4 purged with high-
purity N2 as electrolyte solution. A Pt plate was used as the counter electrode and a
saturated calomel electrode (SCE) was used as the reference electrode. The potentials
in this work were quoted with respect to reversible hydrogen electrode (RHE). In 0.5
M H2SO4, E (RHE) = E (SCE) + 0.26 V. The working electrode was a glassy carbon
(GC, 4 mm diameter), it was polished with slurry of 0.3 μm and 0.05 μm alumina
successively and washed ultrasonically in deionized water prior to use. The working
electrode was prepared as follows: firstly, 5 mg of the catalyst was dispersed
ultrasonically in 525 μL solutions containing of 25 μL Nafion® solution (5 wt%) and
0.5 mL ethanol solution; secondly, 5 μL catalyst inks was pipetted and spread on the
glassy carbon disk; at last, the electrode was obtained after the solvent volatilized with
the catalyst loading was 0.379 mg cm-2. Cyclic voltammetry (CV) curves were
recorded in a potential window between 0.30 and 1.40 V, and the scanning rate
ranged from 2 to 300 mV s-1 in N2-saturated solution. The charge (Q) was calculated
from the different voltammograms of various scanning rates, by the following
equation:
S5
(1)𝑄 =
𝐸2
∫𝐸1
|𝑗|𝜈
𝑑𝐸
where j is the current density obtained from CV curves, v is the scanning rate ranged
from 2 to 300 mV s-1, and E is the scanning potential between 0.70 and 1.40 V. Linear
sweep voltammetry (LSV) curves for OER were recorded in a potential window
between 1.10 and 1.70 V at a potential scanning rate of 5 mV s-1 in N2-saturated
solution at room temperature.
Turnover frequency (TOF) calculation of the catalysts: The TOF value was calculated
from the equation1,2:
(2)𝑇𝑂𝐹 =
𝑗 × 𝐴4 × 𝐹 × 𝑛
where j is the current density at a given potential, A is the surface area of the electrode,
F is the Faraday constant (a value of 96485.3 C mol-1), and n is the number of moles
of metal on the electrode. All the Ir and Ru atoms were assumed to be accessible for
catalyzing the OER.
Ohmic drop was corrected using electrochemical impedance spectroscopy (EIS)
methods according to the equation:
(3)𝐸𝑎 = 𝐸𝑏 ‒ 𝐼𝑅𝑠
where Ea is the potential after I-R correction, Eb is the potential before I-R correction,
I is the corresponding current and Rs is the resistance of the system obtained from EIS
plots as the first intercept of the main arc, all data have been corrected for 90% iR
potential drop. The EIS were recorded on an Autolab potentiostat in the frequency
range of 0.1 Hz to 10 kHz at the potential of 1.55 V, a 10 mV amplitude of sinusoidal
S6
potential perturbation was employed in the measurements. The chronoamperometric
(CA) experiments were performed in N2-saturated 0.5 M H2SO4 solution at 1.60 V to
estimate the performance degradation of the catalysts N2-saturated. The accelerated
durability tests (ADTs) were performed to assess the catalyst durability by applying
cyclic potential sweeps between 1.10 and 1.70 V at a sweep rate of 50 mV/s for 3000
cycles in N2-saturated H2SO4 solution at room temperature.
Two electrode configuration for overall water splitting tests were performed with
the as-prepared anodic catalysts and commercial Pt/C (20 wt%Pt) catalyst were used
to catalyze the OER and HER in acidic solution, respectively. The loading of anodic
catalysts on the electrode was 1.0 mg cm-2 and the loading on cathode was 2.0 mg cm-
2. The LSV experiments were performed with a potential window ranged from 0.5 to
3.0 V at a scanning rate of 10 mV s-1 in 0.5 M H2SO4 at room temperature.
S7
2 Supplementary Tables and Figures
Fig. S1 TEM images and HRTEM images of (a, d) IrO2-RuO2@Ru (1:1), (b, e) IrO2-
RuO2@Ru (2:1) and (c, f) IrO2-RuO2@Ru (4:1).
Fig. S2 HAADF and the corresponding elemental mapping images of (a) IrO2-
RuO2@Ru (1:1), (b) IrO2-RuO2@Ru (2:1) and (c) IrO2-RuO2@Ru (4:1).
S8
Fig. S3 EDX patterns of (a) IrO2-RuO2@Ru (1:1), (b) IrO2-RuO2@Ru (2:1), (c) IrO2-
RuO2@Ru (3:1), (d) IrO2-RuO2@Ru (4:1) and (e) Ir3RuO2.
S9
Fig. S4 XRD patterns of metallic Ru and Ru-oxidated after heat treatment under 450
°C in air.
S10
Fig. S5 XPS spectra of IrO2-RuO2@Ru (3:1) and Ir3RuO2 within the binding energy
range between 600 and 200 eV.
S11
Table S1. Theoretical and actual value of Ir:Ru on the surface of IrO2-RuO2@Ru
(1:1), IrO2-RuO2@Ru (2:1), IrO2-RuO2@Ru (3:1), IrO2-RuO2@Ru (4:1), IrO2 and
Ir3RuO2.
Catalyst Ir:Ru (theoretical value) Ir:Ru (actual value)
IrO2-RuO2@Ru (1:1) 1:1 9.01:3.14 (2.87)
IrO2-RuO2@Ru (2:1) 2:1 8.17:2.09 (3.91)
IrO2-RuO2@Ru (3:1) 3:1 8.1:1.3 (6.23)
IrO2-RuO2@Ru (4:1) 4:1 9.08:1.37 (6.63)
IrO2 --- ---
Ir3RuO2 3:1 6.14:2.11 (2.91)
Table S2. XPS analysis of IrO2-RuO2@Ru (1:1), IrO2-RuO2@Ru (2:1), IrO2-
RuO2@Ru (3:1) and Ir3RuO2.
Catalyst Assignment Position (eV) Intensity (%)
Ru (0) 461.7 31.3IrO2-RuO2@Ru (1:1)
Ru (IV)-RuO2 463.7 68.7
Ru (0) 461.8 39.0IrO2-RuO2@Ru (2:1)
Ru (IV)-RuO2 463.9 61.0
Ru (0) 462.2 55.8IrO2-RuO2@Ru (3:1)
Ru (IV)-RuO2 464.4 44.2
Ru (0) 462.8 33.1Ir3RuO2
Ru (IV)-RuO2 464.5 66.9
S12
Fig. S6. (a) Cyclic voltammetry curves at the scanning rate of 50 mV s-1, (b) The
reversibility of redox and charging process, (c) Dependence of the voltammetric
charges on the scanning rates of 2-300 mV s-1, and (d) The rations of outer charge to
total charge of IrO2-RuO2@Ru (1:1), IrO2-RuO2@Ru (2:1), IrO2-RuO2@Ru (3:1),
IrO2-RuO2@Ru (4:1), IrO2 and Ir3RuO2 catalysts at the scanning rate of 300 and 2
mV s-1 in N2 saturated 0.5 M H2SO4 at room temperature. Catalyst loading: 0.379 mg
cm-2.
S13
Fig. S7. Linear sweep voltammetry curves of (a) IrO2-RuO2@Ru (1:1), (b) IrO2-
RuO2@Ru (2:1), (c) IrO2-RuO2@Ru (3:1), (d) IrO2-RuO2@Ru (4:1), (e) IrO2, (f)
Ir3RuO2, (g) IrO2 (CM) and (h) RuO2 (CM) in N2 saturated 0.5 M H2SO4 at room
temperature. Catalyst loading: 0.379 mg cm-2. Solid and dashed lines represent
polarization curves without and with iR-corrected.
S14
Table S3. Electrocatalytic analysis of linear sweep voltammetry curves.
Catalyst Overpotential/10 mA cm-2
IrO2-RuO2@Ru (1:1) 312
IrO2-RuO2@Ru (2:1) 299
IrO2-RuO2@Ru (3:1) 281
IrO2-RuO2@Ru (4:1) 301
IrO2 317
Ir3RuO2 293
IrO2 (CM) 318
RuO2 (CM) 289
S15
Table S4. Electrocatalytic analysis of linear sweep voltammetry curves for IrO2-
RuO2@Ru (3:1) and IrO2 with different catalyst loadings and current densities.
Catalyst Overpotential/0.5 mA cm-2
Overpotential/1 mA cm-2
Overpotential/5 mA cm-2
Overpotential/10 mA cm-2
IrO2-RuO2@Ru (3:1)-0.379 mg
cm-2212 227 267 283
IrO2-RuO2@Ru (3:1)-0.279 mg
cm-2212 234 273 291
IrO2-RuO2@Ru (3:1)-0.179 mg
cm-2223 244 283 304
IrO2-RuO2@Ru (3:1)-0.100 mg
cm-2234 254 295 316
IrO2-RuO2@Ru (3:1)-0.079 mg
cm-2242 260 301 324
IrO2-0.379 mg cm-2 241 261 300 319
S16
Table S5. Comparison of OER overpotential for IrO2-RuO2@Ru (3:1) with other
electrocatalysts in acidic media.
Catalyst ElectrolyteCatalyst loading(mg cm-2)
Current density(j, mA cm-2)
Overpotential @ j (mV vs. RHE)
Overpotential @ j (mV vs.
RHE; iR-corrected)
References
0.5 211 211
1 227 227
5 268 266
IrO2-RuO2@Ru (3:1)
0.5 M H2SO4
0.379
10 283 281
This work
Ir0.7Co0.3
OX
0.5 M H2SO4
0.102 0.5 ~260 - 3
Ir0.67Sn0.3
3O2
0.5 M H2SO4
0.948 5 25 vs. SCE - 4
Ru0.8Ir0.2
O2
0.5 M H2SO4
0.38 10 >320 - 5
Ir0.5Ru0.5
O2
0.5 M H2SO4
0.204 10 ~320 - 6
IrOx/SrIrO3
0.5 M H2SO4
- 10 - 270-290 7
Ir0.5Ru0.5
O2/ATO0.5 M H2SO4
0.8 1 - 240 8
IrO2/Nb0.
05Ti0.95O2
0.5 M H2SO4
0.255 1 200-300 - 9
IrO2/Nb-TiO2
0.1 M HClO4
0.23 10 ~310 10
S17
Table S6. Electrocatalytic analysis of Tafel plots.
Catalyst Tafel slope
IrO2-RuO2@Ru (1:1) 55.6 mV/dec
IrO2-RuO2@Ru (2:1) 56.2 mV/dec
IrO2-RuO2@Ru (3:1) 53.1 mV/dec
IrO2-RuO2@Ru (4:1) 56.2 mV/dec
IrO2 57.3 mV/dec
Ir3RuO2 56.5 mV/dec
S18
Table S7. The quantitative analysis of Ir, Ru dissolution after ADTs by ICP-OES.
CatalystOriginal Ir/Ru
ratio(EDX)
Ir-dissolution
percentage from Ir
component(at%)
Ru-dissolution
percentage from Ru
component(at%)
IrO2-RuO2@Ru
(1:1)1.03:1 19.8 31.7
IrO2-RuO2@Ru
(2:1)1.92:1 15.4 24.1
IrO2-RuO2@Ru
(3:1)2.94:1 8.3 14.2
IrO2-RuO2@Ru
(4:1)3.89:1 10.6 17.3
IrO2 -- 12.8 --
Ir3RuO2 2.97:1 17.7 28.2
S19
References
1. F. Song and X. Hu, J. Am. Chem. Soc., 2014, 136, 16481-16484.
2. L. Trotochaud, J. K. Ranney, K. N. Williams and S. W. Boettcher, J. Am. Chem.
Soc., 2012, 134, 17253-17261.
3. W. Hu, H. Zhong, W. Liang and S. Chen, ACS Appl. Mater. Interfaces, 2014, 6,
12729-12736.
4. G. Li, H. Yu, X. Wang, S. Sun, Y. Li, Z. Shao and B. Yi, Phys. Chem. Chem.
Phys., 2013, 15, 2858-2866.
5. N. Mamaca, E. Mayousse, S. Arrii-Clacens, T. W. Napporn, K. Servat, N. Guillet
and K. B. Kokoh, Appl. Catal. B, 2012, 111-112, 376-380.
6. L-E. Owe, M. Tsypkin, K. S. Wallwork, R. G. Haverkamp and S. Sunde,
Electrochim. Acta, 2012, 70, 158-164.
7. L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, C. Kirk, A.
Voivodic, H. Y. Hwang, J. K. Norskov and T. F. Jaramillo, Science, 2016, 353,
1011-1014.
8. A. T. Marshall and R. G. Haverkamp, Electrochim. Acta, 2010, 55, 1978-1984.
9. W. Hu, S. Chen and Q. Hua, Int. J. Hydrogen. Energy, 2014, 39, 6967-6976.
10. C. Hao, H. Lv, C. Mi, Y. Song and J. Ma, ACS. Sustainable Chem. Eng., 2016, 4,
746-756.